Help with FXO/FXS POTS wireless link

I've not done anything with voip yet, so pardon if I ask something 'obvious'...

I'm working on extending a regular POTS line across a canyon.

I have a pair of 900mhz ethernet bridge boxes (old Arlan 630 series).

I'd been googling for POTS-over-ethernet or POTS-over-RS232 solutions, and noticed a few hits mentioning VOIP stuff. So I did a few hours of reading and research on VOIP; and got the happy feeling that the hardware I need is already in existence, and pretty reasonably priced as well.

If I understand correctly, I could build my simple "wireless POTS extender" using an FXO and an FXS on either end of my wireless ethernet link; is that correct?

The FXO connects to the phone-company analog POTS wires at the roadside, and it'll have a 10baseT connector for hooking it to one of the Arlan 900mhz boxes.

Across the canyon at the cabin, I would need an FXS (to provide battery and ring voltages to 'recreate' a phone-co style RJ-11 POTS port) and that FXS again simply plugs into the ethernet port on the 2nd Arlan 900mhz box.

Questions:

1) Do I understand the function of FXO/FXS units right?

2) Will the FXO and FXS talk to each other over a simple enet bridge, with no other devices or PC's on the network? (i.e., they are self-controlling? note; I do understand that I'll have to hook a laptop to them once, at install, to do the configs)

3) Do all brands of FXO/FXS speak the same langauge over the enet-link? In other words, will a brand-x FXO hook up with a brand-y FXS without any trouble?

4) Is the line-quality of fxo/fxs as good as a regular POTS line? In other words, it will run 56k modems fine? From what I've read, these fxo/fxs boxes use full 64kbps PCM (same as normal phone-co DS0 line quality).

5) Which Linksys model #'s are best to use? I.e, cheapest, simplest, LOW POWER ?? Or does another brand offer better FXO/FXS for my app (e.g., lower power, cheaper, etc.)

Note: The FXO side boxes must run from solar and battery. No AC power there...and since a PV/batt setup is expensive as hell per watt, I want to make sure I choose the FXO with the lowest power-consumption and one with good power-minimization during on-hook standby.

6) Does a wireless FXO/FXS product already exist? Even wifi (2.4g) might work for this app; especially if the boxes had conns for external ants. The path is very close to LOS, and less than 1,000'.